A unique sequence located downstream from the rice mitochondrialatp6 may cause male sterility

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Abstract
Asymmetric cell-fusion of the japonica cultivar ofOryza sativa (rice) with cytoplasmic-male-sterile (CMS) plants bearing cytoplasm derived from Chinsurah Boro II, resulted in two classes of cytoplasmic hybrids (cybrids), fertile and CMS. Southern-blot analysis of the mitochondrial DNA (mtDNA) indicates recombination events around a number of genes; however, the appearance of the CMS character is tightly correlated to reorganization around theatp6 gene, suggesting recombination downstream from theatp6 gene is involved in CMS. The nucleotide sequence downstream fromatp6 contains a pseudogene which was probably created by recombination of the mitochondrial genome. Sense and antisense transcripts of the downstream region ofatp6 were found in CMS-and restored CMS (fertile)-lines, but not in the normal (fertile) line. In the CMS line, several antisense transcripts of theatp6 gene were also found. However, in the restored line which contains a nuclear-encoded gene,Rf-1, the levels of these transcripts were lower than in the CMS line. These results suggest abnormal transcripts of theatp6 gene produced in the antisense direction may be involved in CMS, and that products of the nuclear-encoded restorer gene may reduce abnormal transcription in this region of the mitochondrial genome.